Many recreational water sports use buoyant bodies such as surfboards, body boards, and skis to allow the user to glide across the surface of the water. To provide an element of control, fins are mounted to the base of the buoyant bodies, generally towards the rear.
With regard to surfboards, modern fins are provided as assemblies which are removably coupled to the underside of the surfboard. Other fins are formed with the surfboard, though such fins are difficult to repair and provide no distinct advantages over removable fins.
Fins in general serve to direct the flow of water so as to stabilise the buoyant body and allow it to be controlled by the user. This stability is largely afforded by preventing rotation of the rear of the body, so that the rear of the body follows the front of the body as it is directed by the user. Thus the body cannot simply rotate. However, by preventing rotation, fins also make it exceedingly difficult to perform tricks, such as 360° turns and slides, for which rotation is desirable. Such manoeuvres can generally only be performed with luck or by an experienced and skilful surfer applying sufficient force with appropriate timing and positioning of weight on the body.
Desired, therefore, is a fin assembly that prevents rotation so as to provide control over the buoyant body, but that also allows substantially unhindered rotation to afford manoeuvrability and tricks to be performed.